Everything You (N)ever Wanted to Know About Varroa Mites

by Bespoke Bee SupplyAugust 21, 2018

Hive losses? There mite be a problem!

As a beekeeper, educator, and co-owner of Bee & Bloom, the topic of honey bees comes up “organically” on a regular basis. I’ve found that every Uber driver and their mother has at least one bee anecdote locked and loaded in response. Above all, I’ve heard tales of countless grandfathers (never grandmothers oddly enough) keeping bees, eliciting bouts of nostalgia and stories detailing eating raw honeycomb straight from the hive. What most people don’t realize, however, is that beekeeping is a radically different undertaking these days due to a number of factors. As you might imagine, some examples include a lack of varied and nutritional forage, and overuse of pesticides (especially systemic pesticides like neonics). Sneaky and unsuspecting, the mother of all problems modern beekeepers deal with is a tiny parasitic mite known as Varroa destructor. In this post I will cover what varroa mites are, how they affect honey bees, and will outline the major philosophies practiced by beekeepers to deal with them.

Originally an obligate parasite to Apis cerana (Asian honey bee), varroa mites were introduced to North America sometime in the 1980’s, after it jumping hosts to Apis mellifera (European honey bee). Varroa mites are external parasites that get transmitted from worker bee to worker bee, or picked up from flowers by foragers. When returned to the hive, they drop off their bee taxi, and enter brood cells where they feed on fat bodies of the developing bee, and reproduce. After a full life cycle, one pregnant female varroa mite can leave behind up to 6 offspring, the females of which are already pregnant by the time they emerge from the brood cell, and are ready to start the lifecycle over again. In this way, they spread like wildfire. Now, we can confidently speculate that they are present in every hive in North America. Even if you don’t see them running around in your hive, they are there. Most of the mite population will be enclosed within developing brood cells, and those that aren’t will be wedged in between scales underneath the bees’ abdomens.

If weakening their hosts by feasting on their fat bodies wasn’t enough, these mites often vector viruses in the process. When mites cause colony losses, it is usually due to a conglomeration of the viruses they vector and weakened immune systems that increase their susceptibility to fungal and bacterial diseases naturally present in the hive. This is known as parasitic mite syndrome (PMS), or varrosis. A 2010 study by Neumann and Carreck outlined the effects of mites on hive losses across the world, and stated that 30% of America’s managed colonies died from varrosis in 2009 and 2010.

Faced with unprecedented colony losses after the introduction of varroa mites, beekeepers unloaded the firepower of the chemical treatment industry on their hives. While this seemed to work for a time, killing mites to a nearly undetectable level, they came back with a vengeance. To make things worse, those previously effective treatments no longer worked. These days, beekeepers must face the fact that varroa mites aren’t going anywhere, and we need to learn how to live with them in our hives at manageable levels. The way beekeepers do this will generally place them into one of three philosophical categories: conventional, treatment free, and practitioners of integrated pest management (IPM).

Bee with DWV, deformed wing virus (Bee & Bloom, 2017)

Conventional beekeepers are either practicing at a commercial scale, maintaining thousands of hives for commercial pollination, or are hobbyists simply following commercial beekeeping standards. These beekeepers will use any tool or chemical treatment available to keep as many of their hives alive as possible. Beekeepers working at the commercial scale will often not have the time or capability to check each colony’s health. They will instead follow a treatment schedule which caters to the average, treating every colony with antibiotics and miticides when they would expect those problems to be at their worst. This is born from a lack of bandwidth and high stakes in the commercial beekeeping sector. These beekeepers are contracted to have a certain number of their hives brought out for pollination events, and if they have significant colony losses, they stand to lose a lot money. This beekeeping method, particularly when mimicked by hobbyists has ramifications including mites developing resistance to treatments, and bees developing a reliance on their keepers and the treatments they use in order to survive. Thus, we’ve entered into an arms race in which we elicit the use of stronger and stronger synthetic and organic chemicals to ensure hive survival.

On the opposite side, the main weapon treatment-free beekeepers are invoking against mites is the genetics of their bees. The idea is that if allowed to coexist with varroa mites with minimal intervention, honey bees will eventually develop a natural resistance to their effects. In the short term these beekeepers expect high colony losses, allowing the weakest colonies to die, and only the strongest colonies to survive. In the long term, the strongest surviving bees will spread their mite-resistant genetics via swarming and colony splits. The goal is to produce a honey bee strain that can manage mites, or any environmental pressure that may cause colony losses, on their own, without human intervention. This is best accomplished when beekeepers have a large number of colonies to draw from, and can repopulate dead hives by splitting strong, surviving colonies. Some prominent beekeepers that practice this philosophy include: Michael Bush, Solomon Parker, and Hillary Kearny.

Many hobbyist treatment-free beekeepers with only a few hives may find that their bees die several years in a row. Unless they are repopulated with swarms, they must start over with bees ordered from commercial producers year after year, or they may give up entirely. Thus, the genetic experiment may never end up having an impact, and the keepers may never end up benefiting from their beekeeping efforts via harvesting hive products, or simply having the satisfaction of keeping their bees alive. A kind of middle ground between these two extreme philosophies, and one that I recommend to most hobbyists, is following integrated pest management practices. The goal of this method of beekeeping is to increase colony survival by using a combination of management tools, including cultural practices, mechanical treatments (eg: the use of robbing screens), and synthetic or organic chemical treatments when necessary. Practitioners of IPM will monitor their hives for mites, and will only respond with treatments when mite populations have reached certain thresholds. Thus, only hives that are in danger will be treated, and strong chemicals will only be used as a last resort. To learn more about IPM, and varroa management, and so much more follow Bee & Bloom’s blog.

In the Bee & Bloom apiaries, we manage a high number of colonies, and use IPM techniques including monitoring for mites, and responding with cultural and mechanical treatments. When mite populations reach threshold levels, we may treat with powdered sugar shakes, initiate brood breaks with queen cages, use drone foundation to trap and remove mites in brood cells, and we always prevent robbing with robbing screens or entrance reducers. Our hive numbers give us leeway for colony losses, so we never use synthetic or organic chemical treatments on our bees. We go into every season expecting to lose some hives to mites, but do our best to keep them from spreading, and in the long term, expect to have a functioning apiary with honey bee stock that can survive with minimal intervention.

Bee & Bloom beekeepers monitor each hive in their apiary for mites, and note their populations throughout the season so they know how to respond, and whether their treatments are working.

Over time, every beekeeper will come up with a combination of practices that works best for them, and those practices may indeed change over time. It takes years to learn to read a hive’s health, and many hobbyists plan to begin their beekeeping endeavors by following IPM with the long term goal of transitioning into treatment-free practices. Ultimately, you will find a method of mite control you feel most comfortable with. For example, if your one hive has such high mite levels varrosis is inevitable, maybe you’re willing to break out a strong chemical treatment to keep them alive, and that is something no one should look down on you for. The weight of saving the honey bee does not rest on the shoulders of any one hobbyist, and each beekeeper will find their balance.

Guest blogger Rebekah Golden is one third of Bee & Bloom. Beekeepers and native pollinator advocates in Portland, OR, Bee & Bloom runs two educational apiaries and an online resource that covers the many facets of working with bees. They hold classes and hands-on workshops on all bee-related topics, and offer management and consultation services to beekeepers throughout the Portland area.

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